This invention relates to the manufacture of a shaft made of a composite material, and, more particularly, to the manufacture of such a shaft suitable for use as a golf club shaft.
One type of advanced golf club shaft is hollow and is made of graphite/epoxy composite material. To manufacture such a shaft by a know approach, a mandrel is prepared with an outside diameter of about the inside diameter of the hollow shaft Pieces of material, sometimes termed "flags" or "laminates", made of a prepreg composite meaterial are successively rolled onto the mandrel to build up several layers. The flags are applied in such a fashion that they adhere to the mandrel and to each other sufficiently to permit the buildup of multiple layers. A compaction tape is wound over the rolled flags The mandrel and tape are heated to elevated temperature. The compaction tape applies an external pressure to the flags of composite material, compressing them against the mandrel. With further heating, the epoxy of the composite material cures to form a final cured product. Following curing, the mandrel is removed. Other fabrication techniques such as external or internal bladders and molds may instead be used
In an application under development by the inventor, a collar must be affixed to the external surface of the shaft. In one approach known in the art for affixing a collar to the external surface of a shaft and illustrated in FIG. 2 of U.S. Pat. No. 5,277,423, an inner diameter of the collar overlies an outer diameter of the composite material. In another approach illustrated in FIG. 4 of the same patent, a outer diameter of the collar is flush with the outer diameter of the composite material.
As noted in the '423 patent the approach of FIG. 4 has the advantage that it provides a uniform cross-sectional diameter for the shaft. However, it presents a problem in manufacturing the shaft Although the '423 patent does not disclose any manufacturing method for making the FIG. 4 embodiment, it appears from FIG. 4 that a recess is ground into the outer surface of the composite material, and the collar, presumably furnished as two semicylindrical segments, is positioned into the recess and fastened there adhesively. In another approach, the collar could be positioned in the recess of an external female mold and the composite material deformed into the female mold and around the collar by an applied internal presure such as produced by a bladder inside the shaft.
While perhaps operable, each of these manufacturing approaches has distinct disadvantages. The most important disadvantage of using a two-piece collar is that the collar may debond and fall away from the shaft during service, which is unacceptable for a premium product. The most important an disadvantages of the internal pressurizing approach are that an internal bladder is required, that the reinforcement of the composite material must deform around the collar so that the basic internal structure of the shaft is disrupted, and that the approach is more expensive.
There is a need for an improved approach to the manufacture of a composite shaft having an eternal collar, preferably a continuous collar, attached flush with the surface of the shaft. The present invention fulfills this need, and further has related advantages.